Electrically Evoked Compound Action Potential Thresholds Research Articles

Predicting most comfortable listening levels of ESRT from ECAP thresholds in paediatric cochlear implant users.

Studies have reported a varied correlation strength between the electrically evoked compound action potential (ECAP) and electrically evoked stapedial reflex thresholds (ESRT) in cochlear implant recipients. However, there is a lack of information on the relationship between the two measures in paediatric cochlear implant users. This study was aimed to compare the ESRT and ECAP measures and determine where ECAP thresholds fall within the dynamic range of ESRT-based Maps in paediatric cochlear implant users. The study involved 40 children aged between 3 and 6 years and were implanted with MedEL cochlear implant device unilaterally. ESRT and ECAP thresholds were measured for all twelve electrodes during the same mapping session, three months after cochlear implant activation. The results revealed significant differences between ECAP and ESRT thresholds across all electrodes. A significant moderate correlation between ESRT and ECAP thresholds was observed on all electrodes. The ECAP thresholds could predict the ESRT based Most comfortable levels (MCLs) significantly. Notably, ECAP thresholds fell by 17-34% from the upper stimulation levels of ESRT-based maps across the electrodes. This study's findings have significant implications for programming cochlear implants in paediatric patients. For children who are unable to cooperate during ESRT measurements, or in cases where ESRT cannot be elicited, ECAP measurements offer a viable alternative. ECAP-based estimates can be used to set MCL levels that closely approximate those derived from ESRT, ensuring appropriate stimulation levels for these young children using cochlear implants.

Influence of Cochlear Anatomy on Intraoperative Electrically Evoked Compound Action Potentials.

Objective: The electrically evoked compound action potential (ECAP) is an objective measure to indirectly assess spiral ganglion neurons. The ECAP provides inputs about the prognoses of cochlear implant (CI) recipients. Several factors such as cochlear morphology can affect ECAP measurements. This study aims to investigate the variation effect of cochlear parameters on intraoperative ECAP thresholds. Methods: This is a retrospective study on patients who underwent CI surgery with normal inner ear morphology at our center between 2017 and 2023. Cochlear anatomical parameters, including diameter (A value), width (B value), and height (H value), as well as cochlear duct length (CDL), were measured pre-operatively using OTOPLAN software (Version 3.0). Cochlear implant intraoperative objective measures were also collected. The correlation between the cochlear parameters and intraoperative objective measures was studied. Results: A total of 45 patients underwent cochlear implantation. The mean age was 2.4 ± 0.9 years. The mean CDL and cochlear coverage values were 33.2 ± 2.0 mm and 76.0 ± 5.7%, respectively. The ECAP threshold increased toward basal electrodes, with ECAP values as follows: apical 13.1 ± 3.8; middle 14.3 ± 3.7; and basal 15.6 ± 4.8. Additionally, the A, B, and H values showed a positive correlation with ECAP thresholds in different cochlear regions. The B value showed a significant moderate correlation with ECAP thresholds in the middle and basal electrodes but not in the apical electrodes. Conclusions: Cochlear anatomical parameters correlate with intraoperative ECAP thresholds. The B value showed a significant association with ECAP thresholds in the middle and basal electrodes. These findings could delineate the impact of the B value in CI and optimize electrode selection. Further research is required to study this correlation and its impact on postoperative outcomes.

Intraoperative Compound Action Potentials as a Predictor of Postoperative Cortical Auditory Evoked Potentials in Cochlear Implant Users.

Electrically evoked cortical auditory evoked potentials (ECAEPs) are central brain responses to auditory stimuli that correlate with postoperative cochlear implant (CI) hearing outcomes. They differ from electrically evoked compound action potentials (ECAPs) which are peripheral responses that can be elicited intraoperatively and may also predict CI hearing outcomes. It is not known to what degree ECAP and ECAEP responses are associated with each other. Such a correlation, if present, may allow for an earlier and more accurate prediction of postoperative hearing outcomes. This retrospective study involved 42 adult CI users. Threshold levels and amplitude growth function slopes of intraoperative ECAPs were compared to the latencies and peak-to-peak amplitudes of postoperative ECAEP responses at three different cochlear electrode array sites (apical, medial, and basal). A weak positive relationship was found between intraoperative ECAP thresholds and ECAEP N1-P2 peak-to-peak amplitude (r = 0.301, p = 0.005). Time between ECAP and ECAEP measurements was weakly correlated with P1-N1 peak-to-peak amplitude (r = 0.321, p = 0.002) and ECAEP N1-P2 peak-to-peak amplitude (r = 0.340, p = 0.001). ECAP amplitude growth function slopes varied by electrode location (χ2 = 26.701, df = 2, p = 0. 000002). These results suggest that intraoperative ECAP responses do not robustly predict postoperative ECAEP responses, providing caution against the use of ECAPs as a predictive tool for CI hearing outcomes.

The Inter-Phase Gap Offset Effect as a Measure of Neural Health in Cochlear Implant Users With Residual Acoustic Hearing.

The inter-phase gap (IPG) offset effect is defined as the dB offset between the linear parts of electrically evoked compound action potential (ECAP) amplitude growth functions for two stimuli differing only in IPG. The method was recently suggested to represent neural health in cochlear implant (CI) users while being unaffected by CI electrode impedances. Hereby, a larger IPG offset effect should reflect better neural health. The aims of the present study were to (1) examine whether the IPG offset effect negatively correlates with the ECAP threshold and the preoperative pure-tone average (PTA) in CI recipients with residual acoustic hearing and (2) investigate the dependency of the IPG offset effect on hair cell survival and intracochlear electrode impedances. Seventeen adult study participants with residual acoustic hearing at 500 Hz undergoing CI surgery at the University Hospital of Zurich were prospectively enrolled. ECAP thresholds, IPG offset effects, electrocochleography (ECochG) responses to 500 Hz tone bursts, and monopolar electrical impedances were obtained at an apical, middle, and basal electrode set during and between 4 and 12 weeks after CI surgery. Pure-tone audiometry was conducted within 3 weeks before surgery and approximately 6 weeks after surgery. Linear mixed regression analyses and t tests were performed to assess relationships between (changes in) ECAP threshold, IPG offset, impedance, PTA, and ECochG amplitude. The IPG offset effect positively correlated with the ECAP threshold in intraoperative recordings ( p < 0.001) and did not significantly correlate with the preoperative PTA ( p = 0.999). The IPG offset showed a postoperative decrease for electrode sets that showed an ECochG amplitude drop. This IPG offset decrease was significantly larger than for electrode sets that showed no ECochG amplitude decrease, t (17) = 2.76, p = 0.014. Linear mixed regression analysis showed no systematic effect of electrode impedance changes on the IPG offset effect ( p = 0.263) but suggested a participant-dependent effect of electrode impedance on IPG offset. The present study results did not reveal the expected relationships between the IPG offset effect and ECAP threshold values or between the IPG offset effect and preoperative acoustic hearing. Changes in electrode impedance did not exhibit a direct impact on the IPG offset effect, although this impact might be individualized among CI recipients. Overall, our findings suggest that the interpretation and application of the IPG offset effect in clinical settings should be approached with caution considering its complex relationships with other cochlear and neural health metrics.

Association Between Intracochlear Electrode Design and Electrically-Evoked Compound Action Potential Measures in Cochlear Implant Users.

Cochlear implant (CI) electrode design has changed over time. Changes in intracochlear electrode design might influence the spread of neural activation along the auditory nerve and the number of independent channels. This study aimed to investigate the impact of intracochlear electrode design on the electrode-neuron interface using electrophysiological measures. Prospective cohort study. A single tertiary hospital. Fifty-two ears who were implanted with CI divided into 3 groups based on the design of intracochlear electrode arrays. Twenty-three ears were implanted with lateral wall straight electrodes. Eighteen ears were implanted with the slim perimodiolar electrode, and 11 ears were implanted with the old perimodiolar electrode. Various electrically-evoked compound action potential (ECAP) metrics were measured to quantify spread of excitation and channel interaction. ECAP threshold and slope were not significantly different among groups. ECAP spread of excitation (SOE) half-width and channel interaction index (CII) were significantly larger in subjects implanted with the lateral wall straight electrodes, indicating a wider spread of excitation compared to those with perimodiolar electrodes. Electrode impedance was significantly lower in subjects implanted with perimodiolar electrodes than those with lateral wall electrodes. Perimodiolar electrode groups yielded significantly narrower SOE half-widths and smaller CII than the lateral wall straight electrode group. This may indicate that the electrode array that hugged the modiolus had less overlap in neural excitation between adjacent electrodes, resulting in reduced channel interaction and potentially better spectral resolution than the electrode array positioned more laterally.

Prediction of Cochlear Implant Fitting by Machine Learning Techniques.

This study aimed to evaluate the differences in electrically evoked compound action potential (ECAP) thresholds and postoperative mapping current (T) levels between electrode types after cochlear implantation, the correlation between ECAP thresholds and T levels, and the performance of machine learning techniques in predicting postoperative T levels. Retrospective case review. Tertiary hospital. We reviewed the charts of 124 ears of children with severe-to-profound hearing loss who had undergone cochlear implantation. We compared ECAP thresholds and T levels from different electrodes, calculated correlations between ECAP thresholds and T levels, and created five prediction models of T levels at switch-on and 6 months after surgery. The accuracy of prediction in postoperative mapping current (T) levels. The ECAP thresholds of the slim modiolar electrodes were significantly lower than those of the straight electrodes on the apical side. However, there was no significant difference in the neural response telemetry thresholds between the two electrodes on the basal side. Lasso regression achieved the most accurate prediction of T levels at switch-on, and the random forest algorithm achieved the most accurate prediction of T levels 6 months after surgery in this dataset. Machine learning techniques could be useful for accurately predicting postoperative T levels after cochlear implantation in children.

The Effect of Electrode Position on Behavioral and Electrophysiologic Measurements in Perimodiolar Cochlear Implants.

The shape and position of cochlear implant electrodes could potentially influence speech perception, as this determines the proximity of implant electrodes to the spiral ganglion. However, the literature to date reveals no consistent association between speech perception and either the proximity of electrode to the medial cochlear wall or the depth of insertion. These relationships were explored in a group of implant recipients receiving the same precurved electrode. This was a retrospective study of adults who underwent cochlear implantation with Cochlear Ltd.'s Slim Perimodiolar electrode at the Royal Victorian Eye and Ear Hospital between 2015 and 2018 (n = 52). Postoperative images were obtained using cone beam computed tomography (CBCT) and analyzed by multi-planar reconstruction to identify the position of the electrode contacts within the cochlea, including estimates of the proximity of the electrodes to the medial cochlear wall or modiolus and the angular depth of insertion. Consonant-vowel-consonant (CVC) monosyllabic phonemes were determined preoperatively, and at 3 and 12 months postoperatively. Electrically evoked compound action potential (ECAP) thresholds and impedance were measured from the implant array immediately after implantation. The relationships between electrode position and speech perception, electrode impedance, and ECAP threshold were an analyzed by Pearson correlation. Age had a negative impact on speech perception at 3 months but not 12 months. None of the electrode-wide measures of proximity between electrode contacts and the modiolus, nor measures of proximity to the medial cochlear wall, nor the angular depth of insertion of the most apical electrode correlated with speech perception. However, there was a moderate correlation between speech perception and the position of the most basal electrode contacts; poorer speech perception was associated with a greater distance to the modiolus. ECAP thresholds were inversely related to the distance between electrode contacts and the modiolus, but there was no clear association between this distance and impedance. Speech perception was significantly affected by the proximity of the most basal electrodes to the modiolus, suggesting that positioning of these electrodes may be important for optimizing speech perception. ECAP thresholds might provide an indication of this proximity, allowing for its optimization during surgery.

ART and AutoART ECAP measurements and cochlear nerve anatomy as predictors in adult cochlear implant recipients

PurposeThe purpose of this retrospective study is to compare the results of electrically evoked compound action potential (ECAP) measurements using automatic auditory response telemetry (AutoART) with those obtained by ART in adults. The study also aimed to evaluate the predictive value of intraoperative ART and AutoART ECAPs for speech intelligibility (SI) and hearing success (HS), and to determine if cochlear nerve (CN) cross-sectional area (CSA) obtained preoperatively by magnetic resonance imaging (MRI) scans could predict ART and AutoART ECAPs and SI and HS outcome.MethodsThe study analyzed and correlated ART and AutoART ECAP thresholds at electrodes E2, E6, and E10, as well as averaged ECAP thresholds over electrodes E1–E12, using data from 32 implants. Correlations were also examined for ART and AutoART ECAP slopes. In addition, averaged ART and AutoART ECAP thresholds and slopes over all 12 electrodes for each participant were correlated with CN CSA measured from MRI sequences. SI of the monosyllabic Freiburg Speech Test at 65 dB sound pressure level was examined along with averaged ART and AutoART thresholds and slopes over all 12 electrodes. A parallel analysis was performed for HS, derived from the difference between baseline and 6-month SI. Finally, correlations between CN CSA and SI, as well as CN CSA and HS were examined.ResultsThe results of the study showed a significant positive correlation between ART and AutoART ECAP thresholds and as well as slopes for E2, E6, E10 and averaged thresholds and slopes of E1–E12. However, no significant correlation was observed between ART and AutoART averaged ECAP thresholds and slopes and either SI and HS or CN CSA. Furthermore, no significant correlation was found between CN CSA and SI and HS.ConclusionWhile AutoART is a reliable and safe program for measuring ECAPs in adults, the study found no preoperative prognostic information on intraoperative ECAP results using parameters extracted from current MRI sequences or pre-/intraoperative information on subsequent hearing outcome using ECAP and CN CSA.

The Effects of Stimulus Repetition Rate on Electrically Evoked Auditory Brainstem Potentials in Postlingually Deafened Adult Cochlear Implant Recipients.

Background: By using outcome prediction scores, it is possible to distinguish between good and poor performers with cochlear implants (CI) after CI implantation. The reasons for poor performance, despite good basic conditions, can be manifold. On the one hand, the postoperative fitting may be inadequate; on the other, neurophysiological disease processes may impair speech understanding with a CI. These disease processes are not yet fully understood. In acoustics, it is known that the auditory brainstem responses (ABR) and their latencies and amplitudes allow differential diagnosis based on reference values for normal-hearing individuals. The aim of this study was to provide reference values for electrically evoked brainstem responses (EABRs) in terms of rate-dependent latencies and amplitudes. Methods: 20 ears of 18 experienced adult CI recipients with a predicted and measured good postoperative word recognition score were recruited from the clinic's patient pool. In the same stimulation mode and intensity we measured latencies and interpeak-latencies of EABRs and electrically evoked compound action potentials (ECAPs). With a defined supra-threshold stimulation intensity above the individual ECAP threshold, we applied stimulation at several rates between 11 and 91 stimuli per second. Results: We found rate dependences for EABR latency t3 and t5 in the order of 0.19 ms and 0.37 ms, respectively, while ECAP was not affected by rate. Correspondingly, the interpeak intervals' rate dependences for t5-t1, t5-t3 and t3-t1 were of the order of 0.37 ms, 0.18 ms and 0.19 ms. Comparing the EABR amplitudes between the stimulation rates 11/s and 81/s, we found that at 81/s the amplitudes were significantly reduced down: to 73% for A3 and 81% for A5. These rate dependences of latency and amplitude in EABR have characteristics comparable to those of acoustic ABR. Conclusions: These data may serve to provide reference values for EABR and ECAP latencies, interpeak intervals and amplitudes with respect to stimulation rate. Altered response patterns of ECAPs and EABRs to normalised stimulation modes could be used in the future to describe and classify neuropathological processes in a better-differentiated way.

Electrically evoked compound action potentials in cochlear implant users with preoperative residual hearing.

Residual hearing in cochlear implant (CI) candidates requires the functional integrity of the nerve in particular regions of the cochlea. Nerve activity can be elicited as electrically evoked compound action potentials (ECAP) after cochlear implantation. We hypothesize that ECAP thresholds depend on preoperative residual hearing ability. In a retrospective study, we analyzed 84 adult cochlear implant users who had received a Nucleus® CI632 Slim Modiolar Electrode and who preoperatively had had residual hearing. Inclusion criteria were severe to profound hearing loss with preoperative measurable hearing in the ear to receive the implant, postlingual hearing loss, German as native language and correct placement of the electrode, inserted completely into the scala tympani. Electrically evoked compound action potential (ECAP) was recorded intraoperatively. The angular insertion was measured for each electrode contact from postoperative computed tomography to estimate the corresponding spiral ganglion frequency. Pure-tone audiometry and allocated ECAP thresholds were tested to investigate possible correlation. The average of hearing thresholds, tested at 0.5, 1, 2, and 4 kHz (4FPTA) was 82 ± 18 (range 47-129) dB HL. The success rate for recording ECAP thresholds was 96.9%. For all comparable pure-tone frequencies (1, 2, 4, and 8 kHz), there was significant correlation between preoperative hearing levels and intraoperative ECAP thresholds (p < 0.001). Higher hearing thresholds are associated with increased ECAP thresholds. In CI candidates with adequate residual hearing, intraoperative electrophysiological measurement records lower thresholds. This outcome may be explained by the neural survival density of the peripheral system, with less neural degeneration.

Facilitation properties in electrically evoked compound action potentials depending on spatial location and on threshold

Spiral ganglion neurons (SGNs) facilitation properties can be recorded utilizing electrically evoked compound action potential (ECAP). While intracochlear variation of the ECAP threshold in relation to its electrode channel is reported, no study investigated its impact on facilitation. In this study, we quantified intracochlear variation of the facilitation properties in cochlear implants (CI) using ECAPs. We hypothesized that the facilitation effect is dependent on the electrode channel and its ECAP threshold. Therefore, ECAPs were recorded in 23 CI subjects. For each subject, five default (channel-derived) and up to two additional (threshold-derived) stimulation sites were defined. Facilitation was quantified by the paradigm introduced by (Hey et al., 2017) with optimized parameter settings. For each channel the maximum facilitated amplitude was determined by a series of ECAP measurements. A linear mixed-effects model was used to investigate the impact of the electrode channel and ECAP threshold on the maximum facilitated amplitude. The maximum facilitated amplitude was found to be dependent on the ECAP threshold and independent on the electrode channel. We conclude that the facilitation paradigm is a useful and feasible tool to gain local information on the SGNs temporal processing patterns.

Features of processor fitting in patients with different types of cochlear implant electrode array

Introduction. The results of cochlear implantation in patients with bilateral sensorineural hearing loss are influenced by many factors, including the type of electrode array. The location of the electrodes in relation to neurons of spiral ganglion affects on levels of perception of the patient's hearing sensations.Aim. To evaluate the dependence of electrically evoked compound action potential (ECAP) thresholds values and comfortable levels depends on electrode array type.Materials and methods. 26 patients with bilateral sensorineural hearing loss with cochlear implantation systems were examined. The patients were divided into 2 groups: 1) patients with a straight electrode array (n = 14); 2) patients with a perimodiolar electrode array (n = 12). We tested speech intelligibility and ECAP thresholds. The difference in the values of both parameters was estimated.Results. For both groups of patients, the relationship between the threshold's profiles of ECAP thresholds and maximum comfortable stimulation levels was detected. For patients from the first group (straight electrode array), the differences in values between the studied parameters were 30.6 ± 6.1%. In patients from the second group, the differences in the values of the thresholds for ECAP thresholds and the levels of comfortable stimulation ranged 2.4 ± 2.1%.Conclusion. The perimodiolar electrode array is located closer to the neurons of the spiral ganglion, which may explain the greater relationship between the values of the ECAP thresholds and the levels of comfortable stimulation. This pattern must be considered when programming the processor of the cochlear implantation system.

Characteristics of responsiveness of cochlear nerve to electrical stimulation in patients with cochlear nerve deficiency

Objectives: This study aimed to evaluate the responsiveness of cochlear nerve to electrical stimulation in patients with cochlear nerve deficiency(CND), to compare their results with those measured in implanted children with normal-sized cochlear nerves, and to investigate the characteristics of the cochlear nerve injury of children with CND. Methods: Participants were children who underwent cochlear implantation at Shandong Provincial ENT Hospital from January 2012 to January 2020, including CND group and control group. The CND group included 51 subjects (male:20; female: 31) who were diagnosed with CND and had normal cochlea. For the CND group, four children had been bilaterally implanted, the mean implantation age was (2.7±1.5) years old. The control group included 21 subjects (male:10; femal:11) who had normal-sized cochlear nerve and normal cochlea. For the control group, all children had been unilaterally implanted except one, and the mean implantation age was (3.0±1.9)years old. Three subjects in the CND group used CI422 electrode arrays, and all the other subjects used CI24RECA/CI512 electrode arrays. The electrically evoked compound action potentials (ECAP) had been tried to record for each electrode using Custom Sound EP software (v. 4.3, Cochlear Ltd.) at least six months post first activation. Furthermore, ECAP amplitude growth functions (AGF) were measured at multiple electrode locations across the electrode array. Generalized linear mixed effect models with the subject group and electrode location as the fixed effects and subjects as the random effect were used to compare results of ECAP measurements. Results: In the control group, ECAP could been recorded at all electrodes (100%), but it could only be recorded in 71% (859/1 210) electrodes in the CND group. Additionally, the percentage of electrodes with measurable ECAP decreased from electrode 1 to electrode 22 in the CND group. Compared to the control group, the ECAP thresholds significantly increased, the ECAP amplitudes and AGF slopes significantly decreased, and the ECAP latency significantly increased in the CND group (P<0.01). GLMM showed that the stimulating site had a significant effect on the ECAP threshold, maximum amplitude, and AGF slope (P<0.01), but had no significant effect on the ECAP latency (P>0.05) in the CND group. However, the stimulating site had no significant effects on the ECAP measurements in the control group. Furthermore, the functional status of cochlear nerve varied greatly among CND group. From electrode 1 to electrode 22, the ECAP thresholds gradually increased, the ECAP maximum amplitudes and AGF slopes gradually decreased in the CND group. Conclusion: Compared with patients with normal-sized cochlear nerve, not only the number of residual spinal ganglion neurons reduce,but also the function of spinal ganglion neurons damages in CND patients. The degree of cochlea nerve deterioration varies greatly among CND patients. Generally, the deterioration of cochlear nerve tends to increase from the basal to the apical site of the cochlea.

Audiogram Configuration, Molecular Etiology, and Outcome of Cochlear Implantation in Postlingual Auditory Neuropathy Spectrum Disorder.

To explore the diverse molecular etiologies of postlingual auditory neuropathy spectrum disorder (ANSD) and report on the electrically evoked compound action potential (ECAP) thresholds and the outcome of cochlear implantation (CI). Patients with late-onset, progressive hearing loss who went through molecular genetic testing were enrolled. Type of sensorineural hearing loss (SNHL) was classified as flat, reverse-slope, midfrequency, downsloping, or ski slope. We identified postlingual ANSD subjects through diagnostic tracts applied differently depending on the degree of SNHL. For CI recipients, individual ECAP thresholds, postoperative speech perception abilities, and the genetic cause were analyzed. The detection rate of ANSD among patients with postlingual SNHL was 5.1% (15/293 probands). Diverse genetic etiologies were identified in 7 (46.6%) of the 15 postlingual ANSD subjects, the genetic cause being found exclusively in subjects with reverse-slope SNHL. The pattern of intraoperative ECAP responses was also diverse and showed some correlation with the genetic etiology. Despite the diverse molecular etiology and ECAP responses, CI in postlingual ANSD patients, including those with features involving the postsynaptic component, yielded significant improvements in speech understanding. This study proposes a differentiated diagnostic approach that focuses on both poor speech discrimination and reverse-slope hearing loss for the diagnosis of ANSD. Based on the improvement of speech understanding from all cochlear implantees with ANSD as well as the correlation between the genetic etiology and ECAP thresholds, we suggest that CI can significantly benefit ANSD subjects even those with unknown etiologies unless there is overt peripheral neuropathy.

Relationship between electrically evoked compound action potential thresholds and behavioral T-levels in implanted children with cochlear nerve deficiency

It is challenging to program children with cochlear nerve deficiency (CND) due to limited auditory and speech abilities or concurrent neurological deficits. Electrically evoked compound action potential (ECAP) thresholds have been widely used by many audiologists to help cochlear implant programming for children who cannot cooperate with behavioral testing. However, the relationship between ECAP thresholds and behavioral levels of cochlear nerve in children with CND remains unclear. This study aimed to investigate how well ECAP thresholds are related to behavioral thresholds in the MAP for children with CND. This study included 29 children with CND who underwent cochlear implantation. For each participant, ECAP thresholds and behavioral T-levels were measured at three electrode locations across the electrode array post-activation. The relationship between ECAP thresholds and behavioral T-levels was analyzed using Pearson’s correlation coefficient. The results showed that ECAP thresholds were significantly correlated with behavioral T-levels at the basal, middle, and apical electrodes. ECAP thresholds were equal to or higher than the behavioral T-levels for all tested electrodes, and fell within MAP’s dynamic range for approximately 90% of the tested electrodes. Moreover, the contour of the ECAP thresholds was similar to the contour of T-levels across electrodes for most participants. ECAP thresholds can help audiologists select stimulation levels more efficiently for children with CND who cannot provide sufficient behavioral response.

Effect of inner ear malformations on intraoperative ECAP thresholds and postoperative auditory performance.

ObjectivesThis study sought to characterize the influence of inner ear malformations (IEMs) on intraoperative electrically evoked compound action potential (ECAP) and auditory performance to better understand the underlying pathophysiology related to variabilities in cochlear implant (CI) outcomes that individuals with malformed cochlea may present.MethodsThe medical records of 222 ears implanted with Cochlear Nucleus CI were reviewed. Of the total, 64 ears had radiologic evidence of IEMs, and 158 ears were normal. Individuals with IEMs were grouped based on the severity of anomalies; 38 had mild IEMs (e.g., enlarged vestibular aqueduct, incomplete partition type II, etc.) and 26 had severe IEMs (e.g., cochlear nerve hypoplasia, common cavity, etc.). Intraoperative ECAP thresholds obtained via neural response telemetry (NRT) and the categories of auditory performance (CAP) scores measured at 12 months postoperative were compared and correlated.ResultsAbsent ECAP responses were more apparent in the IEM group. ECAP thresholds were significantly elevated in the severe IEM group, while the mild IEM group had ECAP thresholds comparable to the normal group. The mild IEM group achieved CAP scores similar to the normal control. Patients in the severe IEM group showed significantly lower CAP scores at 12 months postoperative. Significant negative relationships existed between ECAP thresholds and CAP scores obtained from all subjects.ConclusionMeasurable ECAP responses and NRT thresholds varied across groups. The inverse relationship between NRT thresholds and CAP scores may suggest that electrophysiological responses measured during surgery may potentially be indicative of postoperative performance in our CI population.Level of Evidence2b.

Value of Preoperative Imaging Results in Predicting Cochlear Nerve Function in Children Diagnosed With Cochlear Nerve Aplasia Based on Imaging Results.

This study aimed to assess the function of the cochlear nerve using electrically evoked compound action potentials (ECAPs) for children with cochlear implants who were diagnosed with cochlear nerve aplasia and to analyze the correlation between preimplantation imaging results and ECAP responses. Thirty-five children diagnosed with cochlear nerve aplasia based on magnetic resonance imaging (MRI) were included. Preimplantation MRI and high-resolution computed tomography (HRCT) images were reconstructed, and the width of the bone cochlear nerve canal (BCNC), the diameter of the vestibulocochlear nerve (VCN), and the diameter of the facial nerve (FN) were measured. ECAP input/output (I/O) functions were measured at three electrode locations along the electrode array for each participant. The relationship between ECAP responses (including ECAP threshold, ECAP maximum amplitude, and slope of ECAP I/O function) and sizes of the BCNC and VCN was analyzed using Pearson's correlation coefficients. Our analysis revealed that ECAP responses varied greatly among individual participants. Overall, ECAP thresholds gradually increased, while maximum amplitudes and ECAP I/O function slopes gradually decreased, as the electrode location moved from the basal to the apical direction in the cochlea. ECAP responses exhibited no significant correlations with BCNC width or VCN diameter. The ratio of the VCN to FN diameters was significantly correlated with the slope of the ECAP I/O function and the maximum amplitude. BCNC width could not predict the function of the cochlear nerve. Compared with the absolute size of the VCN, the size of the VCN relative to the FN may represent an indicator for predicting the functional status of the cochlear nerve in children diagnosed with cochlear nerve aplasia based on imaging results.

Forward Electric Stimulation-Induced Interference in Intracochlear Electrocochleography of Acoustic Stimulation in the Cochlea of Guinea Pigs.

Electric-acoustic stimulation (EAS) uses amplified sound by a hearing aid to stimulate an apical low-frequency region of the cochlea and electrical current from a cochlear implant (CI) to stimulate the basal high-frequency region. EAS recipients had significantly improved speech perception, music appreciation, and hearing function in noise compared to those relying on CI electrical stimulation (ES) alone. However, the interaction between basal ES and apical acoustic stimulation (AS) in the cochlea potentially affects EAS advantages. To investigate ES-AS interaction, we designed a system that recorded the electrically evoked compound action potential (ECAP) and the auditory evoked potential (AEP). We used an intracochlear electrode array to deliver ES at the basal cochlea and detect intracochlear electrocochleography (iECochG) generated from apical AS. Within iECochG, 3 or 6 dB (double or quadruple intensity of ECAP threshold) electric stimulation, 1 ms-forward ES significantly increased CAP amplitudes of 4 kHz/20 dB AS compared to 0 dB ES. Notably, 1 ms-forward 3 dB ES significantly increased CAP amplitudes of 4 kHz/20 dB AS, while 3 or 5 ms-forward ES did not change the CAP amplitudes. The elevation in CAP amplitude of 40 dB/4 kHz AS induced by 1 ms-forward 3 dB ES was significantly lower than that in 20 dB/4 kHz AS. With 1 ms-forward 3 dB ES, AS frequency and stimulating electrode location have no significant impact on relative CAP amplitudes of 20 dB AS. These results suggest that the basal forward ES and the following apical AS could produce a cumulative effect on the auditory nerve response.

Investigating the association of electrically-evoked compound action potential thresholds with inner-ear dimensions in pediatric cochlear implantation

ObjectivesA narrow bony cochlear nerve canal (BCNC), as well as a hypoplastic and aplastic cochlear nerve (CN) have been associated with increased electrically-evoked compound action potential (eCAP) thresholds in some studies, suggesting poorer neural excitability in cochlear implantation. Also, in large cochleae the extent of activated spiral ganglion neurons with electrical stimulation is less than in smaller ones. However, a detailed description of the relationship between eCAP thresholds for a lateral-wall electrode array and dimensions of the inner-ear structures and internal auditory canal (IAC) is missing. DesignThe study subjects were 52 pediatric patients with congenital severe-to-profound hearing loss (27 females and 25 males; ages 0.7–2.0 years; 1.0 ± 0.3 years, mean ± SD) implanted bilaterally with Cochlear Nucleus CI422, CI522, or CI622 implants with full insertion of the Slim Straight electrode array. Diameters of the cochlea and the BCNC as well as the widths and heights of the IAC and the CN were evaluated from preoperative computed tomography and magnetic resonance images. These anatomical dimensions were compared with each other and with the patients’ intraoperative eCAP thresholds. ResultsThe eCAP thresholds increased from the apical to basal direction (r = 0.89, p < 0.001). After sorting the cochleae into four size categories, higher eCAP thresholds were found in larger than in smaller cochleae (p < 0.001). With similar categorization, the eCAP thresholds were higher in cochleae with a larger BCNC than in cochleae with a smaller BCNC (p < 0.001). Neither IAC nor CN cross-sectional areas affected the eCAP thresholds. Correlations were found between cochlea and BCNC diameters and between IAC and CN cross-sectional areas (r = 0.39 and r = 0.48, respectively, p < 0.001 for both). ConclusionsIn the basal part of the electrode array, higher stimulation levels to elicit measurable neural responses (eCAP thresholds) were required than in the apical part. Increased eCAP thresholds associated with a larger cochlear diameter, but contrary to the earlier studies, not with a small size of the BCNC or the CN. Instead, the BCNC diameter correlated significantly with the cochlea diameter.

Toward a method of achieving balanced stimulation of bilateral auditory nerves: Evidence from children receiving matched and unmatched bilateral cochlear implants simultaneously

ObjectivesTo identify whether mismatched bilateral cochlear implants compromise balanced stimulation of the two auditory nerves and establish asymmetric hearing in children. MethodsBehavioural and electrophysiological measures were completed in 47 children receiving bilateral CIs in the same surgery (simultaneously): 27 children received a peri‑modiolar N24RE array in one ear and a 422 anti-modiolar array in the other (experimental group) and 20 children received 2 peri‑modiolar arrays (control group). Differences in current levels between the two devices were measured by electrically evoked compound action potentials (ECAPs) at the time of surgery. These data were compared with minimum and maximum comfortably loud levels programmed in each speech processor (T-levels, C-levels, respectively) after 12 months of bilateral CI use. Asymmetries in functional hearing between arrays were measured in open set speech perception testing between 3 to 5 years of CI use. ResultsHigher current levels were required from the anti-modiolar than peri‑modiolar array to evoke balanced interaural ECAP amplitudes (mismatched group: mean ± SD difference: -9.9 ± 22.6; matched group: -0.8 ± 26.5). This difference was larger in the experimental group than control group (t = -2.51; p = 0.016) and remained constant with increases in current level from ECAP threshold to maximum amplitudes (dynamic range) in many but not all children in both groups. T and C-levels were poorly predictive of levels needed to evoke balanced ECAP amplitudes in children with mismatched devices (F(1, 312) = 1.3, p = 0.263). Speech perception scores were more asymmetric between ears in children using bilateral mismatched arrays (mean ± SD: 73.8 ± 16.4 at the peri‑modiolar array; 57.7 ± 26.4 at the anti-modiolar array), compared to children with bilateral matched arrays (right ear: 78.0 ± 10.4; left ear: 74.9 ± 13.5). ConclusionHigher current level requirements at the anti-modiolar array compared to the peri‑modiolar array in children with bilateral mismatched CIs are not fully accounted for in device programming. Mismatched electrodes in children receiving bilateral cochlear implants increases the risk of asymmetric hearing.